Protecting surface for a steel lithographic plate



Patented May 18, 1948 PROTECTING SURFACE FOR A STEEL LITHQGRAPHIC PLATE Charles H. Van Dusen, Jr., Willoughby, Ohio, assignor to Addressograph-Multlgraph Corporation, Wilmington, Del., [corporation of Delaware No Drawing; Application July 1, 1942,

, Serial No. 449,349

3 Claims. (Cl. 101-14938) This invent-ion relates to a lithographic or planographic printing plate and to a method of making the same.

An object of the present invention is to afiord a new thin, flexible metal lithographic or pianographic printing plate which is relatively more wear-resistant than the metal and other lithographic or planographic printing plates heretofore and now employed in the art and has, therefore, a relatively longer useful or image-reproducing life; which may be employed for lithographic image reception by either the so-called direct image or by the photographic process; which is highly resistant to and does not tend to pick up finger prints from the oily secretion of the skin upon handling with resultant spotting of the reproduced images as may happen 'in the use .of aluminum lithographic printing plates, especially when the latter have been mechanically grained to provide the desired image-receptive lithographic printing surface thereon; which does not require chemical treatment with an oxidizing or other agent to provide the desired image-receptive surface thereon and hence does not tend to lose on image aillxed thereto, during use, due to loss of oxide fllm as may occur in the use of aluminum lithographic printing plates which have been treated with an oxidizing agent to provide the desired image-receptive etched printing surface thereon; which does not necessitate the use of a, so-called counteretching process to remove oxide film prior to use as do zinc lithographic printing plates, which is thin and flexible and may, therefore, be readily installed and used upon the drums of modem rotary duplicating and printing machines employing the offset lithographic reproduction process; which may readily be provided with a rust-inhibitive coating which when applied does not need to be removed and does not interfere in any way with the image-receptive properties of, nor with the use of, the new lithographic or planographic printing plate in the lithographic or planographic reproduction process; and which has the other a ntages and desirable characteristics which are herein described or which are inherent in the new lithographic printing plate.

Another object of the invention is to effect and realize a novel and efficient method of making the new thin, flexible metal lithographic or pianographic printing plate. I

An additional object of the invention is to effect and realize a novel combination of steps the new plate in such a manner as to assure the absence of such hook-shaped or like objectionable ink-retaining portions thereon.

Heretofore in the art, various materials have been employed in the manufacture of lithographic or planographic printing plates and among these have been aluminum and zinc and specially prepared paper or like cellulosic materials.

In the case of aluminum lithographic or planographic printing plates which have been mechanically grained to provide the desired image-receptive surface thereon there is a tendency for such plates to pick up and retain finger prints. Since such finger prints are due largely to the plates coming into contact with the fatty secretion of the skin one objectionable result thereof is that the thus spotted portions of such aluminum plates become ink-receptive and tend to form ink spots on the copies during the lithographic or planographic reproduction process.

In the use of zinc lithographic or planographic printing plates, it is desirable, before forming and affixing a desired image thereon by either the direct image-reception or the photographic image-reception process, to subject such zinc plates to a process known as counteretching, which consists in washing the surface of the zinc plate with an acid solution to effect the removal of the oxide coating formed thereon by exposure of the plate to air and moisture, since otherwise the image might tend to come off from the plate if the oxide fllm thereon were not removed before the image is applied.

I have found, however, that very satisfactory lithographic printing plates may be made of steel, or other metals hereinafter referred to, treated in the manner hereinafter described, and that the new lithographic printing plates may be used not only for so-called direct image reception but also in the photographic image-reception lithographic process, and that the new lithographic printing plates are highly satisfactory and efllcient and have good image-reception and good image-reproduction properties and a relatively long image-reproducing life regardless of whether the desired image is formed thereon and afllxed thereto by the direct image-reception process or by the photographic image-reception process.

Moreover, I have found that it is unnecessary to provide the new lithographic printing plates with an oxide film or surface coating since, unlike aluminum lithographic printing plates, it is substantially free of any tendency to pick up finger prints by contact with the fatty secretion of the skin and hence does not need to be given, and does not have, an oxide film or coating which in use will peel or chip of! together with the image affixed thereto.

Furthermore, I have also found that the new lithographic printing plates formed and treated in the manner hereinafter described, do not need to be counteretched" so that one operation the use of the new lithographic printing plates treated in the manner hereinafter described.

The new lithographic printing plates likewise have the additional advantage over aluminum and zinc plates which resides in the fact that they are much harder and more wear-resistant than are aluminum and zinc lithographic plates and hence have a longer useful image-reproducfling life. This, of course, enables relatively longer editions and better copies to be reproduced therefrom.

In endeavoring to find a metallic material which could be used in forming lithographic printing plates which might be employed in place .of both aluminum and zinc lithographic or of the fatty, oily or greasy material employed asthe rolling coolant and which is either embedded or sealed in the steel during the operation of cold rolling the steel stock from which such steel plates were made or which is 'baked upon such steel stock during the operation of bright annealing the same.

I have now found, however, that by properly treating or processing the metal from which the new lithographic or planographic printing plates are made, the formation of spots thereon, as well as the tendency of the plate to "tone up, resulting from working to the surface of the fatty, oily or greasy materials used as the rolling coolant during the rolling operation, and which, being ink-receptive, tends'to pick up ink during the lithographic or planographic reproduction process, may be substantially completely i which may be required in the making of zinc lithographic printing plates may be eliminated in stock of which the new lithographic printing plates are made before it is subjected to the bright annealing operation.

Another serious difficulty encountered in connection with the manufacture of the new steel lithographic printing plates resided in the fact that attempts to mechanically grain only one surface thereof tended to cause objectionable curling of the plates so that the plates thus grained would not lie flat and were not only difficult to handle, but-could not be used commercially. This difllculty, however, was avoided by graining the new lithographic printing plates in the manner, and under the carefully controlled conditions, hereinafter recited.

In the practice of the present invention, and for the purpose of making the new lithographic printing plates, the stock employed is preferably low carbon open hearth cold rolled steel, treated according to known processes, and while the thickness of the completed stock may vary considerably, I have found that steel, for example, approximately 0.002" or 0.003" thick is well suited for use in making the new steel lithographic printing plates. It will be understood in this connection, however, that the thickness of the new lithographic printing plates depends, to a large extent, upon the dimensions of, and available clearances in, the rotary offset lithographic printing or duplicating machines in which the new lithographic printing plates are intended for use, as well as upon whether or not the plates are to be grained upon only one side or upon both sides, upon the degree of flexibility desired in the plates, and upon other variable factors. Thus, for example, if the plates are to be grained upon only one side, the preferred thickness of the stock is as hereinbefore specifled, with an optimum upper limit of from about 0.005" to about 0.010". However. if the plate is to be grained upon both sides the optimum upper limit for the thickness of the steel stock is about 0.025".

The processes involved in preparing the preferred steel stock employed in making the new lithographic printing plates consist, in general, of hot rolling the low carbon open hearth coil steel stock to a thickness of approximately 0.100", then cold rolling the stock in graduated steps to a thickness of, for example, about 0.010", the stock being subjected to a conventional bright annealing operation between successive cold rolling operations, electrolytically cleaning the thus cold rolled stock when it has attained a 7 thickness of, for example, about 0.010", and then further bright annealing and cold rolling the thus treated stock to the desired thickness of the new steel lithographic or planographic printing plates which, as pointed out above, may be, for example, about 0.002" or 0.00

During the operation of further cold rolling the steel stock, after the electrolytic cleaning operation, the surface of the steel becomes thickly coated with the greasy or oily rolling coolant material and one of the rolling coolant'materials, commonly employed is a liquid material consisting of approximately ninety percent mineral oil and ten percent wool fat. However, regardless of the composition of the rolling coolant employed it must be removed from the surface of the selectedsteel stock before the steel stock vis mechanically grained to provide the desired eliminated by electrolytically cleaning the metal accomplished in any suitable manner as, for example, by immersing the steel in a volatile chlorinated hydrocarbon solvent degreaser or by boiling in an alkaline degreasing solution. Thus. for example, the steel may be'satisfactorily degreased by boiling it for a period of from five to ten minutes in a solution made substantially in accordance with the formula disclosed in the following example:

Example After having been boiled in the solution referred to in the foregoing example, and which should preferably be changed from time to time, the plates may be-washed with water and allowed to dry. However, if a volatile chlorinated hydrocarbon solvent is employed as the degreasing agent, in the place of the alkaline degreasing agent which is referred to in the foregoing example, it is merely necessary to immerse the steel stock therein briefly and remove the same therefrom, whereupon the volatile degreasing solvent will, of course, rapidly dry by evaporation so that the washing operation required when using an alkaline degreasing solution is rendered unnecessary. v

The cleansing solution described in the foregoing example is satisfactory for the purpose of cleaning the surface of the coil steel stock, prior to the graining operation, in order to' remove therefrom any oily or fatty materials with which the steel may have become coated during the cold rolling operation subsequent to the electrolytic cleaning operation.

The preferred method of mechanically graining the selected steel stock to provide the desired image-receptive printing surface on the new steel lithographic or planographic printing plates is by subjecting the thin, flexible steel stock. either before or after it is cut to the desired or intended size of the lithographic or planographic printing plates to be made therefrom, to the action of a stream of finely divided abrasive particles, preferably under the action of centrifugal force only, rather than by means of an air blast or the like. and for this purpose I have-found that what is commonly known as steel grit, but is, more exactly,. chilled cast iron containing about 3.20%

, carbon, as combined carbon, and having the following Tyler standard screen scale sieve analysis is quite satisfactory:

Per cent Total Per Mesh Between cent on Each Sieves Sieve 1 All Pass.

ing the graining operation, whereas the steel grit particles remain intact. Moreover, I have found that such breaking up of the sand particles is objectionable because the relatively fine particles of sand thus formed tend to inhibit the graining action due, I believe, to the fact that they are not sufllciently abrasive and cannot be propelled with sufliciently velocity to create or develop the kinetic energy which is required to efi'ect the graining operation in a satisfactory manner.

Moreover subiecting the steel stock to the action of a stream of steel grid under the action of centrifugal force only is preferred over the use of an air blast because of the fact that an air blast tends to create a back wash of abrasive particles which prevents all of the abrasive particles from striking the surface of the steel at substantially the same angle, as will be described presently.

I have found, in this connection, that in order to provide the desired mechanically grained image-receptive surface on the new lithographic or planographic printing plates, and to prevent the same from curling during or as a result of the graining operation, it is necessary to control certain variable factors which are involved in the operation of mechanicall graining the-new metal lithographic printing plates, these variable factors being substantially as follows: l) The thickness of the steel or other metal employed in make ing the new metal lithographic printing or pianographic plates, as well as the specific gravity, hardness, composition, and other properties thereof; (2) the particle size of the steel grit or other abrasive particles employed in the graining operation; (3) the velocity at which the steel grit or other abrasive particles strike the surface of the steel or other metal during'the graining operation; and (4) the concentration of the steel grit or other abrasive particles, that is, the mass or number of the steel grit or other abrasive particles striking a given surface area of the steel or other metal as, for example, one square foot,

i in a given length of time as, for example, one

second, during the graining operation.

In connection with the control of the variable factors which are involved in the graining operation, and to which reference has been made above, I have found, for example, that when employing hard rolled, low carbon, open hearth shim steel stock approximately 0.003" thick in making the new lithographic or planographic printing plates, and when employing steel grit having th screen scale analysis hereinbefore referred to, a rotary centrifugal abrasive particle throwing wheel approximately 33" in diameter, operating in a horizontal plane, and running at a speed of approximately 700 R. P. M. will, during the typical or illustrative graining operation now being described. throw a suflicient quantity or mass of such steel grit particles against the surface of said shim steelstock having the characteristics referred to above to effect satisfactory mechanical graining of said shim steel stock when said steel grit is fed to the center of such a horizontally rotating centrifugal abrasive particle throwing wheel as rapidly as said steel grit particles will flow, by. gravity, through a vertically extending feed pipe or tube approximately 1 in diameter.

While the presentinvention is not limited to the use of any particular apparatus for centrifugally throwing the abrasive particles against the i surface of the steel or like metal during the grain- 7 ing operation. reference may be had to Patents Nos. 2,132,311 and 2,286,754 for a disclosure of suitable rotary centrifugal abrasive particle throwing wheels. either of which may be used to effect the desired mechanical gralning operation, in the practice of the present invention.

It has also been found, in this connection, that substantially all of the steel grit or like abrasive particles employed during the graining operation should strike the surface of the steel or other metal at approximately the same angle, that is, all of the steel grit or like abrasive particles should be thrown by centrifugal force from the periphery of the horizontally rotating centrifugal wheel in such a manner as to strike'the surface of the steel or likemetal stock at approximately the same angle. Moreover, in this connection, I have found that if it is desired to grain a relatively large or wide strip of the selected coil steel stock at one time satisfactory results may be obtained by mounting such a relatively large .or wide strip of coil steel or like metal stock upon the inner surface of a cylindrical support and cyclically moving the vertical support, together with such a relatively large or wide strip of coil steel or other metal stock mounted thereon, alternately vertically up and down past the horizontal plane in which the rotary centrifugal wheel is operated during the gralning operation. However, if it is desired tograin a relativelynarrow strip of the selected coil steel or like metal stock, it is unnecessary to move the same relative to the centrifugal abrasive particle throwing wheel during the gralning operation, whereas a is to move or advance a continuous strip of such metal stock past the rotary centrifugal abrasive particle throwing wheel and through the zone of abrasive particles thrown thereby against the surface of the coil steel or like metal stock.

Moreover, I have found, in this connection, that if the velocity at which the steel grit or other abrasive particles strike the surface of the (steel) stock during the gralning operation is too small or low, a rectangular-shaped piece of steel stock thus grained will tend to curl, both during and after the gralning operation, along its long axis, away from the thus grained surface. On the other hand, I have found that if the velocity at which the steel grit or other abrasive particles strike the surface of the (steel) stock during the graining operation is too great, a rectangularshaped piece of steel stock thus grained will tend to curl, both during and after the gralning operation, along its shorter or transverse axis, in a direction toward the thus grained surface. However, by carefully adjusting and controlling the velocity at which the steel grit or other abrasive particles strike the surface of the steel during the gralning operation so that said velocity is neither too great nor too small, depending, of

course, in part upon thenature, size, density and 7 that is, by giving the stock a relatively heavy or deep grain on one side and a relatively light or shallow grain on the opposite side thereof, it will be appreciated that so doing is costly and uneconomical as a manufacturing operation for eliminating objectionable curling of the plates, which will curl, nevertheless, if grained uniformly on both sides.

It should be noted, in this connection, that the velocity at which the abrasive particles should strike the surface of the steel or like metal stock being grained is inversely proportioned to the size of the abrasive particles employed. Thus, for example, if the abrasive particles are relatively large, withinpermissible limits, the speed of the rotary centrifugal throwing wheel should be relatively slow and, conversely, if the size of the abrasive particles is relatively small, within permissible limits, the speed of the wheel should be relatively fast. v

If the new steel or other metal lithographic printing plates are intended to bei'used within a relatively short time after theyhave been made, and'if proper precautions are taken to prevent rusting as, for example,'keeping the plates in a relatively dry atmosphere, it is not necessary, in the practice of the present invention, to provide them -with a rust-inhibitive coating. However, if the new steel or like metal lithographic or planographic printing plates are intended to be stored for a relatively long or protracted periodof time, after manufacture and before use, and especially in a warm humid climate or atmosphere, I have found that it is preferable to provide the new steel or like metal planographic printing plates with a rust-inhibitive coating, and for this purpose I have found that the new steel .or like metal planographic printing plates may be provided with a satisfactory rust-inhibitive coating by immersing the plates, after they have been mechanically grained, in the manner described above, for a period of approximately 15 seconds in a solution containing approximately 500 parts of sodium chrome glucosate in approximately a'million parts of tap water, at atmospheric temperature. The plates may then be removed from the rust-inhibiting solution and washed and dried, whereupon they are ready for the reception of the desired image by either the direct image-reception process or by the photographic image-reception process, and for use in lithographic or so-called planographic reproduction according to known methods.

The foregoing treatment imparts upon the new steel or like printing plates a rust-inhibitive coating having a thickness of monomolecular proportions and which is substantially free of oily or fatty materials which might be receptive to fatty lithographic inks and thus cause the plates to tone up" in the use thereof.

Moreover, a rust-inhibitive coating of sodium chrome glucosate has the additional desirable characteristic which resides in the fact that it does not interfere with the direct image-receptive, nor with the photographic image-receptive, characteristics of the new lithographic or planographic printing plates, nor with the character or quality of the images or copies, nor with the length of the editions, which may be printed therefrom, in the use of the new steel or like metal lithographic printing plates. Hence, the new lithographic printing plates are highly satisfactory for their intended purposes.

However, in place of the rust-inhibitive surface coating material referred to above, namely,

76 sodium chrome glucosate, other rust-inhibitive of nitrocellulose or ethyl cellulose lacquer which may be peeled ofi or otherwise removed from the new lithographic'printing plate prior to the reception of the desired image upon the plate by either the direct image reception or by the photographic image reception process. However, as pointed out above, sodium chrome glucosate coating has the distinct advantage which resides in the fact that it may be applied to the new mechanically grained lithographic or planographic printing plates after the graining operation and does not need to be removed from the plates before or after the desired image is afflxedthereto by either the direct image reception or the photographic image reception process, and may be allowed to remain upon the plates during their use in the lithographic or planographic printing process. 4

It should be noted, however, that if a rustinhibitive coating containing a fatty or greasy material is employed such coating must be removed from the new plates by a degreasing operation, before the lithographic image is applied thereto, since such fatty or greasy rust-inhibitive material, being ink-receptive, would, of course, interfere with the use of the plates in the lithographic or planographic printing process.

It has been found that when the low carbon open hearth cold rolled coil steel stock from which the new lithographic or planographic printing plates are preferably made is electrolytically cleaned, as described hereinbefore, any oily or greasy material, resulting from contact been subjected to a selected one of the processes referred to above, (electrolytic cleaning, or degreasing and electrolytic pickling), the new steel lithographic printing plates made therefrom will exhibit substantially no tendency to form spots which would otherwise result from the oily or fatty materials embedded in or baked upon the steel bleeding or working to the surface thereof and causing the resulting steel plates to pick up the fatty lithographic inks and tone up during use.

It will, therefore, be seen that the present invention eliminates and overcomes one of the most serious difficulties heretofore involved in the manufacture and use of a steel lithographic or planographic printing plate.

It will further be seen that when the new steel or like metal lithographic or planographic printsuch, for example, as sodium chrom glucosate of monomolecular thickness, as described hereinbefore, rusting of the plates will be inhibited,

while at the same time, this rust-inhibitive coating does not interfere with the formation or reception of the desired image upon the grained surface of the plate, by either the direct imagereception or the photographic image-reception process, nor does it in any way interfere with the image-reproducing properties, nor detract from the useful life of, nor with the length of the editions which may be printed from, the thus coated steel or like metal lithographic or pianographic printing plate.

It will also be noted that when the preferred coil steel stock is grained by centrifugal distribuwith the rolling coolant, which may have become embedded in the steel during the cold rolling operation or which may have been baked thereon during the bright annealing operation is removed therefrom by the electrolytic cleaning process and hence will not later bleed or work to the surface of the steel lithographic printing plate, and cause the plates to "tone up, as would otherwise occur if the steel stock of which the new steel lithographic plates are made were not thus electrolytically cleaned. This is particularly significant in view of the fact that such greasy or oily rolling coolant materials if allowed to remain on the steel stock during the bright annealing operation tends to crack or disintegrate chemically to form a type of "varnish which is extremely dimcult to remove by any degreasing operation, and if allowed to remain on the steel tends to cause spotting thereof after the graining operation.

If desired, however, the coil steel stock employed in making the new printing plates may be subjected to an alternative process for removing the fatty or greasy materials resulting from contact with the rolling coolant, namely, by subjecting the steel stock first to a degreasing operation and then to a known type of electrolytic steel pickling operation, rather than to an electrolytic steel cleaning operation, both of such electrolytic processes being known in the steel industry.

when the steel stock employed therefor has tion of steel grit or like abrasive particles having the particle size and characteristics, and in the satisfactory mechanicallygrained image-receptive surface, and that the plates will lie flat and do not exhibit objectionable curling, even. though grained on only one side thereof. Moreover, the printing surfaces of the plates thus treated or formed will be substantially free of objectionable hook-shaped or like ink-retaining portions which may result if the graining operation is not carried out under the carefully controlled conditions hereinbefore referred to. I have found that such hook-shaped portions are objectionable on the printing surface of the plates because they retain ink and tend to cause the non-image areas of the plate to "tone up" when the plates are in use. Hence, it is desirable that the printing surface of a steel or other metal printing plate be substantially free from such objectionable hook-shaped or like ink-retaining portions or irregularities, and the new printing plates, made according to the practice of the present invention, are substantially free of such portions and hence have this additional desirable characteristic.

While I have hereinbefore specified that low carbon open hearth cold rolled coil steel stock which has been electrolytically cleaned, (or degreased and then electrolytically pickled), as hereinbefore' described, is highly satisfactory for use in making the new lithographic orpianographic printing plates, the present invention is not limited to the use of this specific type of steel since other types of thin. flexible steel such, for example, as stainless steel, (so-called "18-8 and "14), of the same thickness, may be employed in making the new planographic printing plates use of a counteretching solution and operation are. not essential to ,the successful use thereof,

nevertheless, I have found that in certain inv stances the use of such a counteretching solution may be advantageous and particularly where the v advantages of the new. mechanically grained ,planographic printing plates is the fact that the new planographic printing plates are intended for image receptionby the photographic process and, for this purpose, I have found that a suitable counteretching solution may be a concentrated (85%) water solution of phosphoric acid Hence, it will be seen from the foregoing description that the present invention accomplishes 'lts intended objects, including those specifically pointed out above, and aifords a new thin, flexor planographic printing plate which may be used upon the rotary printing or duplicating machines now in use and employing the offset lith- .ographic printing process;-is substantially free of any tendency to pick up finger prints; has highly satisfactory image-reception and imagereproducing characteristics and a relatively longer image-reproducing life than either the zinc lithographic printing plates or the aluminum lithographic printing. plates commonly employed in the art; will lie substantially flat even though mechanically grained on only one side thereof has a printing surface which is substantially free from objectionable hook-shaped or like objectionable ink-retaining portions or irregularities; and which has the related and other desirable advantages and characteristics or properties which have been pointed out hereinbefore or which are inherent therein.

I claim:

1. A thin and normally substantially flat and non-curling flexible steel planographic printing plate having amechanically grained image-receptive surface on at least one face thereof, said image-receptive surface having thereon a rustinhibitive coating comprising sodium chrome glucosate and which is substantially free of any tendency to interfere with the image-reception or. image-reproduction characteristics of said grained image-receptive surface.

.2. A flexible steel planographic printing plate having a grained image-receptive surface on at least one face thereof, said image-receptive surface having thereon a rust-inhibitive coating of sodium chrome glucosate.

3. A steel lithographic printing plate having a lithographic image-receptive surface provided with a. rust-inhibitive coating of sodium chrome glucosate.

CHARLES H. VAN DUSEN, Ja.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 683,572 Norden Oct. 1, 1901 748,004 Pancoast Dec. 29, 1903 749,350 Wunschi Jan. 12, 1904 821,622 Edison May 29, 1906 1,616,358 Fabian Feb. 1, 1927 1,634,658 Flammer' July 5, 1927 1,946,766 Shonkweiler Feb. 13, 1934 2,005,654 Fritsche June 18, 1935 2,042,003 Huebn'er May 26, 1936 2,158,063 Broadfield May 16, 1939 2,204,588 Guite June 18, 1940 2,258,956 Misuiraca Oct. 14, 1941 2,276,594 Rowell Mar, 17, 1943 2,302,669 Batcheller Nov. 24, 1942 2,233,573 Ayers Mar. 4, 1941 2,375,210

Batcheller May 8, 1945 

